Industrial equipment in a factory or the like is normally controlled by a combination starter enclosed in a control cabinet. A combination starter is a single enclosure containing the motor starter, fuses or circuit breaker and a device for disconnecting power. Other devices associated with the control of the motor may also be included. The control cabinet′provides a sturdy metal container holding circuitry to control and/or disconnect power to the equipment and to protect the equipment from excessive current in the event of equipment faults or variations of electrical power.
In many industrial applications, multiple electric motors are required and it is often desirable to control some or all of the motors from a central location. A “motor control center” is a physical grouping of the combination starters or control cabinets physically grouped into one assembly. A motor control center usually is a cabinet holding multiple independent drawers or “buckets”. Each bucket may receive power from a common bus in the cabinet and provide individual disconnect and protection circuitry. By dividing the cabinet into buckets, each motor may have individualized control circuitry and may be separately connected and disconnected from power as may be desired. Typically each bucket has a disconnect operator on its front face that may be operated to disconnect power from the bucket and to provide a mechanical release of the bucket so that the bucket may be removed only when power is disconnected from the bucket.
While the structure of the motor control center provides for good protection against the risk of fire, electrocution and shock hazard, by isolating and disconnecting the buckets when they are extracted, there is recent concern for an additional hazard called arc flash. Arc flash is a result of the electrical arc that super heats the air around it, expanding and creating a pressure wave within an electrical enclosure. The massive heat and energy produced by an arc flash can inflict serious injury including burns from burning and vaporized material, damaged hearing from the sound wave, and impaired eyesight from the high intensity flash. For this reason, personnel working on motor control centers may be required to wear personal protective equipment (PPE) when in the vicinity of a motor control center.
During maintenance of industrial equipment, it is often necessary for maintenance personnel to work on machinery which could pose a hazard if not fully deactivated, or if accidentally reactivated, during maintenance. For this reason, it is known to use lock-out, tag-out (LOTO) procedures to ensure removal of power from such equipment for maintenance. Lock-out, tag-out devices provide a means that positively disconnect power to the associated equipment and which may be locked in the disconnect position with multiple padlocks, one padlock for each maintenance person in the vicinity of the machine. The padlocks provide a simple and reliable mechanism to ensure the machine is not activated accidentally or without the concurrence of all maintenance personnel working on the equipment.
While typically lock-out, tag-out devices are directly attached between the power and the associated machine, alternatively low voltage remote lock-out, tag-out switches have been developed, to be used in conjunction with Safety Isolation Equipment for example the ElectroGuard® safety isolation system commercially available from Rockwell Automation, the assignee of the present application. The system isolation equipment uses a redundantly monitored, remotely operated contactor-isolating system, packaged to provide the disconnection/isolation function. Remote lock-out, tag-out switches permit the operator with its padlocks to be located remote from the main power disconnecting means. This is possible through the use of redundant wiring, safety monitoring relays (having force-guided contacts and a coil structure requiring consistency into redundant inputs for operation) and redundant isolation contactors.
Remote lock-out, tag-out switches and system isolation equipment reduce the time required for maintenance personnel to walk from the machine being maintained to a typically a remote location where power may be disconnected.